1. Field of the Invention
This disclosure is related to the field of polymer interlayers for multiple layer glass panels and multiple layer glass panels having at least one polymer interlayer sheet. Specifically, this disclosure is related to the field of polymer interlayers having improved high flow and reduced thickness or gauge.
2. Description of Related Art
Generally, multiple layer glass panels refer to a laminate comprised of a polymer sheet or interlayer sandwiched between two panes of glass. The laminated multiple layer glass panels are commonly utilized in architectural window applications, in the windows of motor vehicles and airplanes, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. The main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, keep the layers of glass bonded even when the force is applied and the glass is broken, and prevent the glass from breaking up into sharp pieces. Additionally, the interlayer generally gives the glass a much higher sound insulation rating, reduces UV and/or IR light transmission, and enhances the aesthetic appeal of the associated window. In regards to the photovoltaic applications, the main function of the interlayer is to encapsulate the photovoltaic solar panels which are used to generate and supply electricity in commercial and residential applications.
The interlayer is generally produced by mixing a polymer resin such as poly(vinyl butyral) with one or more plasticizers and melt processing the mix into a sheet by any applicable process or method known to one of skill in the art, including, but not limited to, extrusion. Other additional additives may optionally be added for various other purposes. After the interlayer sheet is formed, it is typically collected and rolled for transportation and storage and for later use in the multiple layer glass panel, described below.
The following offers a simplified description of the manner in which multiple layer glass panels are generally produced in combination with the interlayers. First, at least one polymer interlayer sheet is placed between two substrates and any excess interlayer is trimmed from the edges, creating an assembly. It is not uncommon for multiple polymer interlayer sheets to be placed within the two substrates creating a multiple layer glass panel with multiple polymer interlayers. Then, air is removed from the assembly by an applicable process or method known to one of skill in the art; e.g., through nip rollers, vacuum bag, vacuum ring, or another de-airing mechanism. Additionally, the interlayer is partially press-bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding is rendered more permanent by a high temperature and pressure lamination process known to one of ordinary skill in the art such as, but not limited to, autoclaving.
Generally, two (2) common problems are encountered in the art of manufacturing multiple layer glass panels: delamination and bubbling from inefficient de-airing or de-gassing. Delamination is the splitting or separating of the laminate into the individual layers, e.g., the separating of the substrates from the interlayer. This typically occurs around the edges of the multiple layer glass panel and is usually the result of the breakdown of the bond between the glass and the interlayer by atmospheric moisture attack, panel sealant degradation, and/or excessive stress imposed on the glass. Certain conditions tend to accelerate the manifestation of edge delamination, especially when one or more of the substrates is wavy or warped. If the delamination extends too far into the panel, the structural integrity of the glass panel may become compromised.
De-airing or de-gassing is the removal of the presence of gas or air in a multiple layer glass panel. Gas trapped in a multiple layer glass panel can have a negative or degenerative effect on the optical clarity and adhesion of the panel. During the manufacturing process of laminated multiple layer glass panel constructs, gases can become trapped in the interstitial spaces between the substrates and the one or more polymer interlayers. Generally, this trapped air is removed in the glazing or panel manufacturing process by processes such as vacuum de-airing the construct, nipping the assembly between a pair of rollers or by some other method known to those of skill in the art. However, these technologies are not always effective in removing all of the air trapped in the interstitial spaces between the substrates, especially when one or more of the substrates is wavy or warped. Generally, the presence of a gas in the interstitial spaces of a multiple layer glass panel takes the form of bubbles in the polymer interlayer sheet(s) or pockets of gas between the polymer interlayer sheet(s) and the substrates—known as “bubbling”.
Delamination and bubbling are particularly evident and acute when the interlayer is used in conjunction with warped or wavy glass, including, but not limited to, tempered glass, heat strengthened/toughened glass, mismatched glass, bent glass for making windshields, and in photovoltaic applications where additional components are included that cause unevenness. For example, the processing of tempering glass creates some distortion and roller waves, and thus tempered glass is generally not as flat as ordinary annealed glass. In such applications, the waviness of the substrates creates gaps between the substrates themselves and between the substrates and the interlayer(s), resulting in an increased tendency of delamination and bubble formation. Both delamination and bubble formation are undesirable and problematic where the end-product multiple layer glass panel will be used in an application where optical quality or structural integrity is important. Thus, the creation of a near perfect laminated glass essentially free of any gaseous pockets or bubbles is paramount in the multiple layer glass panel manufacturing process. Not only is it important to create a multiple layer glass panel free of gaseous pockets and bubbles immediately after manufacturing, but permanency is also important. It is not an uncommon defect in the art of multiple layer glass panels for dissolved gases to appear (e.g., for bubbles to form) in the panel over time, especially at elevated temperatures and under certain weather conditions and sunlight exposure. More gases or excessive air will be trapped in the laminated panels if glass panels are warped and/or wavy. The excessive air trapped in the laminated panels will significantly reduce the tolerance of the panels for the elevated temperatures and adverse weather conditions, i.e., bubbles could be formed at lower temperatures. Thus, it is also important that, in addition to leaving the laminate production line free from any bubbles or gaseous cavities, the multiple layer glass panel remains gas-free for a substantial period of time under end-use conditions to fulfill its commercial role.
As a measure to prevent delamination and bubbling with warped glass, it has become common to either increase the thickness of the interlayer or the flow of the interlayer (e.g., with an increase in plasticizer loading, or by using a second plasticizer, such as epoxidized vegetable oil alone or in combination with a conventional plasticizer (as disclosed U.S. Patent Application Publication 20130074931A1, the entire disclosure of which is incorporated herein by reference)), or both. Increasing the flow increases the capability of the interlayer to fill the gaps that are inherent in the use of warped or wavy glass substrates. However, there are several problems with some of these interlayer compositions previously utilized in the art. For example, with an increase in thickness comes an increase in both cost and price. With increase in flow may come other problems, including: blocking, plasticizer exudation (if plasticizer loading is too high), creep, surface roughness formation, decreased mechanical strength, and decreased manufacturing capability.
Blocking is generally known to those of skill in the art as the sticking of polymer interlayers to each other. Blocking can be a problem during the manufacturing, storage and distribution of polymer interlayer sheets, where the polymer interlayer sheets (which in most common processes are stored in rolls) come into contact with each other (such as when they are rolled up). When the flow of the interlayer is increased, generally the interlayer becomes more susceptible to blocking, and as a result, it can be difficult, if not impossible, to separate the polymer interlayer sheets.
Creep is the tendency of the solid interlayer material to slowly move or deform permanently under the influence of stresses. Creep can be problematic because multiple layer glass panels tend to become deformed and elongated as a result of the creep of the interlayer. For example, over time the two glass panels may begin to slide apart from one another. The creep will be more problematic if the multiple layer glass panels are not installed in frames or other mechanical devices that attach to both the front and rear glass panel. Rather, only the rear glass panel is attached to a mounting system. The front glass panel (unsupported) relies on the interlayer to carry its weight and maintain structural integrity and durability of the laminated glass. When the panels are positioned vertically or at an angle, it is often a concern that the weight of the unsupported glass panel may experience ‘gravity induced creep’ or shift in certain conditions, such as high temperature climates. The creep performance is affected by the environment where the panels are being installed. For example, if the panel is installed in the tropical zone, it will be exposed to a much higher temperature compared to a non-tropical zone. Generally the creep results from the viscoelastic flow of the polymer with time. In some situations, this creep can result in structural defects and decreased mechanical strength of the interlayer and the resultant multiple layer glass panel. Ideally, there will be very little movement (such as less than 1 mm, or less than 0.5 mm), or even no movement or no creep. Increasing flow comes with an increasing tendency for creep problem.
The surface roughness (characterized as Rz) is generally known to those of skill in the art as the measure of the finer surface irregularities in the texture of the interlayer surface, i.e., peaks and spaces there between on the surface of the interlayer sheet distinguished from the imaginary plane of the flattened polymer interlayer sheet. An appropriate level of surface roughness is needed for good de-airing performance during lamination. If the surface roughness is too low, de-airing will become impossible. On the other hand, if the surface roughness is too high, the large surface irregularities in the interlayer will be difficult to remove during lamination, resulting in more gas being trapped in the multiple layer glass panel. Either too low or too high surface roughness will result in poor de-airing performance and cause more bubbling and delamination, as described above.
The degree of surface roughness is at least in part the result of the manufacturing process employed to create the interlayer. Generally, there are two ways to generate surface roughness during manufacturing: by forming “random rough” surfaces through melt fracture during extrusion (see, for example, U.S. Pat. Nos. 5,595,818 and 4,654,179, the entire disclosures of which are incorporated by reference herein), or by imparting a surface on the interlayer sheet by embossing (see, for example, U.S. Pat. No. 6,093,471, the entire disclosure of which is incorporated by reference herein). Surfaces formed by both methods (that is, both random rough and embossed surfaces) will be affected by the rheological properties (such as flow) of the interlayer. For example, an increase in flow may result in a decrease in the surface roughness formed by melt fracture during extrusion (that is, the surface roughness, Rz, may be too low, which will make de-airing more difficult, causing more bubbling and delamination). Again, such bubbling and delamination is undesirable and can result in visual and structural defects as well as decreased mechanical strength of the interlayer and the resultant multiple layer glass panel. In some extreme cases, surface roughness formed by melt fracture will be extremely low (or the sheet will be very smooth) due to the formulation changes for improving flow because there will be no ‘fracturing’ of the polymer melt to cause the surface irregularities. In such cases where there is very low or no surface roughness level, or even where increased surface roughness is desired (surface roughness levels higher than surface roughness levels formed by melt fracture), embossing techniques have to be employed to produce a surface having a sufficient surface roughness, Rz (such as at least 25 μm, or at least 30 μm, or greater than 30 μm). The embossing process requires additional manufacturing steps and may be a more complicated process, and the end result may be lower efficiency, increased energy costs, and loss of production capacity.
Summarized, delamination and bubbling are common problems in the field of multiple layer glass panels. These common problems are particularly acute when using wavy or warped substrates. In an attempt to correct these problems associated with wavy or warped substrates, it became common to use an interlayer with an increased thickness or flow or both. The increased thickness and/or flow of the previously utilized interlayers, however, resulted in numerous other unfavorable sacrifices, including, but not limited to, increased manufacturing costs (i.e., the costs associated with an increased thickness in the interlayer), blocking, creep, exudation, surface roughness formation, decreased mechanical strength, and decreased manufacturing capability.